Michael additions imides

The Michael addition of nucleophiles to the carbon—carbon double bond of maleimide has been exploited ia the synthesis of a variety of linear polymers through reaction of bismaleimide with bisthiols (39). This method has been used to synthesize ethynyl-terminated imidothioether from the reaction of 4,4 -dimercaptodiphenyl ether [17527-79-6] and A/-(3-ethynylphenyl)maleimide (40). The chemical stmcture of this Michael addition imide thermoset is as follows ... 

The above is an example of the Guareschi reaction. It is applicable to most dialkyl ketones and to alicyclic ketones (e.., cj/clohexanone, cyclopentanone, etc.). The condensation product (I) is probably formed by a simple Knoe-venagel reaction of the ketone and ethyl cyanoacetate to yield ethyl a-cyano-pp dimethylacrylate (CH3)2C=C(CN)COOC2Hj, followed by a Michael addition of a second molecule of ethyl cyanoacetate finally, the carbethoxyl groups are converted to the cyclic imide structure by the action of ammonia. 

Crosslinking of amine- or hydroxy-terminated PAMAM dendrimers using cyclic anhydride - amine or cyclic anhydride - hydroxy addition reactions was employed for preparation of crosslinked thin films of very low permeability [73], Polyanhydrides, such as maleic anhydride-methyl vinyl ether copolymers, were used as crosslinking components. In the case of amine-terminated PAMAM, crosslinking and chemical stability were further increased by imidization of the maleamic acid groups retro-Michael eliminations were followed by Michael additions to further crosslink the film. 

The scope of Michael additions with catalysts containing cyclohexane-diamine scaffolds was broadened by Li and co-workers [95]. When screening for a catalyst for the addition of phenylthiol to a,p-nnsatnrated imides, the anthors fonnd that thiourea catalyst 170 provided optimal enantioselectivities when compared to Cinchon alkaloids derivatives (Scheme 41). Electrophile scope inclnded both cyclic and acyclic substrates. Li attributed the enantioselectivity to activation of the diketone electrophiles via hydrogen-bonding to the thiourea, with simultaneous deprotonation of the thiol by the tertiary amine moiety of the diamine (170a and 170b). Based on the observed selectivity, the anthors hypothesized that the snbstrate-catalyst... 

Scheme 6.69 Products obtained from the 12-catalyzed asymmetric Michael addition of malononitrile, nitromethane, and methyl a-cyanoacetate to N-cinnamoylbenzamide derivatives (acylic imides) and 12-catalyzed derivatization of the Michael adduct.

Scheme 6.70 Mechanistic proposal for the 12-catalyzed asymmetric Michael addition of malononitrile to (J-aryl and alkyl substituted N-acyl pyrrolidinones (cyclic imide) (A) and to a,P-unsaturated N-aryl substituted 2-methoxybenzamides such as N-cinnamoyl-2-methoxybenzamide (acyclic imide) (B).

The Chen group early in 2005 constituted the novel class of thiourea-function-ahzed cinchona alkaloids with the first reported synthesis and application of thioureas 116 (8R, 9S) and 117 (8R, 9R) prepared from cinchonidine and cinchonine in over 60% yield, respectively (Scheme 6.112) [273]. In the Michael addition of thiophenol to an a,(5-unsaturated imide, the thioureas 116 and 117 displayed only poor stereoinduction (at rt 116 7% ee 117 17% ee), but high catalytic activity (99% yield/2h) (Scheme 6.112). 

Scheme 6.112 Michael addition of thiophenol to an a,p-unsaturated imide catalyzed by cinchonidine-derived thiourea 116 and cinchonine-derived thiourea 117, the first representatives of this class of bifunctional hydrogen-bonding cinchona alkaloid-thioureas.

The Michael addition reaction of dimercaptodiphenylether with N-(3-ethynyl phenyl) maleimide allowed the synthesis of ethynyl-terminated imido-thioether as shown in Fig. 50 (139). This acetylene terminated imidothioether was blended with acetylene terminated polyarylene ether oligomers of different molecular weights and tested as composite resins (140). Blends of functionalized thermoplastics such as the acetylene terminated polyarylene ethers with brittle high-Tg imide resins are finding increased attention for tough high-Tg composites. 

A variety of routes for incorporation of the succinimide group into a polymer backbone are provided by the use of bis(maleimide) monomers (8 Scheme 5). Examples include Michael addition of diamines or dithiols (or H2S) to produce poly(imides) (9) (B-80MI11101), and photopolymerization (via the triplet state) to prepare cyclopolymers (10) (73PAC213) having molecular weights of about 30 000. 

FR 2612195 (French) 1988 Thermally stable polymers from bismaleimides, siloxane diamines and optionally maleimide-termi-nated siloxanes Rhone-Poulenc Chimie, Fr. R Barthelemy, Y Camberlin Heat-resistant maleimide-termi-nated siloxane Thermally stable polymers were prepared by co-curing MDA based bismaleimides and male-imide-terminated siloxanes. Michael addition with amino-terminated siloxanes and MDA was also utilized. 

As electron-rich olefins are more reactive, vinyl-sulfones are the most reactive species and are capable of reacting with thiols, amines, and even with small nucleophilic alcohol groups. Less reactive are acrylamides and acrylates, which are reactive towards amines and thiols. Maleimides are the least reactive of the mentioned species and allow selective addition of thiols in the presence of amines in the pH range 6.5-7.5. However, hydrolysis of the imide, especially at elevated pH values [35], may be a concern for certain applications. The mentioned Michael addition reactions do not require organic solvents and can be carried out at physiological temperature and pH [36], In acidic conditions, the reaction is either very slow or does not proceed because protonation removes the nucleophilic form in the case of amines, and the thiolate anion is usually the active species in Michael additions involving thiols [25],... 

Michael Addition. Titanium imide enolates are excellent nucleophiles in Michael reactions. Michael acceptors such as ethyl vinyl ketone, Methyl Acrylate, Acrylonitrile, and f-butyl acrylate react with excellent diastereoselection (eq 21 ). - Enolate chirality transfer is predicted by inspection of the chelated (Z)-enolate. For the less reactive unsaturated esters and nitriles, enolates generated from TiCl3(0-j-Pr) afford superior yields, albeit with slightly lower selectivities. The scope of the reaction fails to encompass p-substituted, a,p-unsaturated ketones which demonstrate essentially no induction at the prochiral center. Furthermore, substimted unsamrated esters do not act as competent Michael acceptors at all under these conditions. 

Various chelated lithium imide enolates have also served as nucleophiles in Michael additions to 3-trifluoromethyl acrylate, favoring the anti isomer (eq 22). ... 

Michael Additions. The Cu[(5,5)-/-Bu-box] (Sbp6)2 complex catalyzes the enantioselective addition of enolsilanes to fu-maroyl imides with enantioselectivities of up to 99% ee and in good yields (up to 91%). Here, the diastereoselectivity correlates with the geometry of the nucleophile ( )-silylketene acetals preferentially deliver anti adducts (eq 16), while (Z)-silylketene acetals afford syn products (eq 17). 

Hoashi Y, Okino T, Takemoto Y (2005) Enantioselective michael addition to alpha, beta-unsaturated imides catalyzed by a bifunctional organocatalyst. Angew Chem Int Ed Engl 44 4032... 

NIR spectrophotometry in the region from 8000 to 4000 cm-1 was used to measure the kinetics of copolymerization of an aromatic bismaleimide (72) derived from an aromatic diamine (e.g. 5a), taking place at 160 to 180 °C. The following NIR spectral ranges were useful for this study primary amine first overtones (vn h) at 7000 to 6400 cm-1, double bond first overtone (vc=c-h) at 6100 cm-1, aromatic first overtones (vc-h) at 6000 to 5750 cm-1, aliphatic first overtones (vc-h) at 5750 to 5350 cm-1 and primary aromatic amine combination bands first overtones (vn h + <5nh2) at 5150 to 4800 cm-1. The process consisted mainly of a second-order Michael addition, as depicted in equation 14, and not the plausible imide opening to yield a maleic dianilide (119), as shown in equation 15. A Michael addition between maleimide moieties and secondary amine moieties present in the products (118) also takes place, however at a rate of about one fourth of that of the primary amine moieties. To improve the SNR of the measurements, usually the results of... 

In 2005, Chen and coworkers found that the epi-cinchonidine/cinchonine-derived thiourea catalysts, 79a,b, can serve as highly active promoters of the Michael addition ofthiophenol to the a,P-unsaturated imide 80 however, the reaction proceeded with low enantioselectivity (up to 17% ee) (Scheme 9.28) [22]. 

Endomethylene tetrahydrophthalic anhydride and the methyl derivate are also claimed for imide formation with aminoethanol [209]. The reaction of the endomethylene tetrahydrophthalic anhydride with hexahydro-p-aminobenzoic acid followed by a esterification with ethylene glycol and terephthalic acid yields an unsaturated imidoester curable by Michael addition with polyamines [210]. 

In addition to these examples of alkylations that employ chelate-enforced intraannular asymmetric induction, Evans s imides are useful in asymmetric aldol (Section 5.2.2 and 5.2.3), and Michael additions (Section 5.3.2), Diels-Alder reactions (Section 6.2.2), and enolate oxidations (Section 8.4), making this one of the most versatile auxiliaries ever invented. 

Amide and imide enolates. Scheme 5.31 illustrates several examples of asymmetric Michael additions of chiral amide and imide enolates. Yamaguchi [163] investigated the addition of amide lithium enolates to -ethyl crotonate, but found no consistent topicity trend for achiral amides. The three chiral amides tested are illustrated in Scheme 5.31a-c. The highest diastereoselectivity found was with the C2-symmetric amide shown in Scheme 5.3Ic. Evans s imides, as their titanium enolates, afforded the results shown in Scheme 5.31d and e [164,165]. The yields and selectivities for the reaction with acrylates and vinyl ketones are excellent, but the reaction is limited to P-unsubstituted Michael acceptors P-substituted esters and nitriles do not react, and 3-substituted enones add with no selectivity [165]. 

Scheme 5.31. Asymmetric Michael addition of amide and imide enolates. (a-c) [163]. (d)...

Scheme 5.40. (a) Wynberg s early example of interligand asymmetric induction in the Michael reaction [201]. (b) Seebach s investigation of cyclohexanone lithium enolate complexed to chiral diamines with extra lithium [3]. (c) Mukaiyama s imide tin enolate and chiral diamine [202]. (d) Mukaiyama s catalytic tin dithioenolate Michael addition [203]. 

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